1. Field of the Invention
This invention relates to the field of magnetic recording. More specifically, this invention relates to thin film heads or data transducers that fly or move closely adjacent to the surface of magnetic recording media on which a magnetic bit pattern is to be written by the head, or which contains a previously written magnetic bit pattern that is to be read by the head. This invention relates to laminated and plated yokes, poles, or pole pieces that form the data transducing magnetic structure of a thin film head.
2. Description of the Related Art
Thin film magnetic heads are generally known in the art. An article entitled NEXT-GENERATION POLE MATERIALS FOR MAGNETIC RECORDING HEADS, pages 61-66 of the publication DATA STORAGE, September 1996, describes thin film heads. An article entitled MR READ HEADS FOR TAPE DRIVES at pages 71-76 of that same publication describes MR heads.
U.S. Pat. No. 5,493,464, to Koshikawa, incorporated herein by reference, describes a sharing type thin film magnetic transducer that includes an inductive write head and an MR read head within one unitary assembly. This device is made up of three pole pieces, the intermediate one of which is shared by a read gap and by a write gap. The pole pieces of this head are not laminated.
A valuable utility of the present invention is to form one or more of the pole pieces of such a sharing type thin film magnetic transducer; for example the shared pole piece, as laminated pole pieces that are constructed and arranged in accordance with the present invention.
Laminated pole piece thin film heads are known wherein adjacent magnetic pole laminations or layers are not separated by an electrically insulating layer as is required by the present invention. Examples are U.S. Pat. No. 5,379,172 to Liao, U.S. Pat. No. 5,264,981 to Campbell, U.S. Pat. No. 4,190,872 to Jones et al, U.S. Pat. No. 4,610,935 to Kumasaka et al, U.S. Pat. No. 4,748,089 to Kumasaka et al; and (4) European Patent Application 0247868 to Kobayashi et al.
It is known that the high frequency magnetic permeability of electrically conductive pole pieces that are within a thin film data transducer is enhanced by limiting the pole piece material thickness to be less than about two times the material's electrical current skin depth at the transducer's operating frequency. By way of example, it is known that at an operating frequency of about 50 mega hertz, the skin depth of an nickel/iron (NiFe) pole piece is about 7000 angstroms.
However, for thin film heads having NiFe yokes, poles or pole pieces, this ideally thin situation requires the NiFe pole pieces be prohibitively thin, for example only somewhat greater than about 14000 angstroms for an operating frequency of about 50 mega hertz. These thin pole pieces, however, provide inadequate conductance of the read or write magnetic flux that is required to flow within the pole pieces.
A solution to this inadequate magnetic flux conduction problem is to laminate the NiFe pole pieces, so as to provide at least two magnetic layers for each pole piece, wherein the two magnetic layers are separated by an electrically insulating layer. To date, the use of laminated pole pieces has been plagued by electrical short circuits that occur between the two adjacent magnetic layers during manufacture of the laminated pole pieces.
By way of example, this lamination short circuiting problem occurs due to side wall redeposition that occurs on the magnetic layers during an ion milling process that is conventionally used to remove a plating seed layer upon which a top magnetic layer has been plated or deposited. This electrically conductive shorting circuit path of redeposited plating seed material is generally quite thin but it is usually greater than about 30 angstroms thick. As a result, this redeposited plating seed path constitutes a relatively low resistance path that provides for the undesirable conduction of eddy currents between the two magnetic layers. This eddy current flow operates to defeat the initial purpose of providing two thin laminated magnetic layers, in that the two layers operate as a single thicker layer in the presence of this eddy current flow.
The need remains in the art for apparatus and/or methods that enable the manufacture and subsequent use of laminated yokes, poles or pole pieces within thin film magnetic MR heads, thin film inductive heads, thin film shared heads, and thin film shared MR/inductive heads, wherein eddy current flow between the magnetic layers of the laminated yokes, poles or pole pieces is eliminated, or at least greatly reduced. More specifically, the need remains in the art for a new and unusual head manufacturing process, and resulting head structure, that enables the head to operate at high frequencies with the advantages that are provided by thin film electrically conductive pole pieces whose individual magnetic thin film thickness is limited to be only somewhat greater than twice the pole material's electrical current skin depth at the head's operating frequency.